1. Field of the Invention
The present invention relates to a pulse-controlled camera of a type in which a basic reciprocating member is successively rotated in a forward direction and in a backward direction by a forward and backward rotational drive force of a a pulse motor. A feeding operation of a photo-taking lens is carried out by the forward rotation of the basic reciprocating member and a shutter mechanism is operated, by the backward rotation to follow. A method for setting a control reference position of the pulse-controlled camera, and to a method for adjusting mechanical errors in production of the pulse-controlled camera are also provided.
2. Description of the Related Art
The pulse-controlled camera of such a type is well known for example as disclosed in Japanese
Laying-open (Kokai) Patent Application No. 62-220939, which was assigned to the same assignee as the present application. The Japanese Laying-open (Kokai) Patent Application No. 62-220939 discloses a technique in which a blade opening and closing ring (reference numeral 13 in the publication) or a drive gear (reference numeral 42 in the publication), which correspond to a basic reciprocating member in the present, invention, are capable of reciprocating. A reference position of the blade opening and closing ring 13, which corresponds to a home position in the present invention, is set as a signal corresponding to an-off motion of a position switch (reference numeral 25 in the publication) comprising a leaf switch, and the blade opening and closing ring 13 is successively rotated in the forward direction and in the backward direction from the reference position to carry out the feeding operation of the photo-taking lens and the exposure operation.
It is necessary in the pulse-controlled camera arranged as above that the blade opening and closing ring 13 is correctly located at the reference position or returned thereto before start of the photo-taking operation or after completion thereof in order to maintain high precision. Such a technique, that is, a technique in which a specific moving member is forced to return to the reference position to maintain the high precision of the camera, is also disclosed for example in Japanese Laying-open (Kokai) Patent Application No. 60-235125.
The Japanese Laying-open (Kokai) Patent Application No. 60-235125 discloses a technique in which, in a shutter device for camera having a step motor (reference numeral 2 in the publication), opening or closing a sector (reference numeral 1 3 in the publication) as a shutter blade, the reference position return detecting means (reference numeral in the publication) is preliminarily provided for detecting that the shutter blade 1 is located at the reference position. The detecting means 3 is used to detect whether the shutter blade 1 is located at the reference position before and after the exposure operation, and if the shutter blade 1 is not located at the reference position then the step motor 2 is rotated in the backward direction to force the shutter blade 2 to return to the reference position, thereby preventing the shutter blade 2 from being left in an open state.
It is normal to make an effort to shorten an overall time necessary for sequence operation as much as possible in case of a camera of a type in which a photo-taking sequence including a feeding operation of the photo-taking lens, an opening and closing operation of the shutter blade, as well as a film feed operation is systematically carried out by making use of a drive force of a motor.
For example Japanese Laying-open (Kokai) Patent Application No. 62-257136 discloses such a technique. The technique as disclosed in the Japanese Laying-open (Kokai) Patent Application No. 62-257136 concerns a compact pulse motor increased in operation speed in which a pulse rate of motor control upon opening and closing of shutter blades is made greater than that upon feeding of a photo-taking lens.
The technique as disclosed in the first Japanese Laying-open (Kokai) Patent Application No. 62-220939 presented various disadvantages. For example, corrosion proceeding or elastic degradation (so-called setting) occurs due to aged deterioration of the elastic leaf because the leaf switch 25 generates the on-off signal by a mechanical operation, whereby occurrence of such abnormal phenomena causes negative effects on the on-off operation and an external factor such as vibrations may make the on-off operation of the switch insecure.
A further problem is that a photographer cannot recognize such abnormal events and continues taking photographs in a qualitatively degraded condition after that.
There are various problems caused in view of production when the leaf switch 25 is employed.
In detail, an actual production causes errors within a tolerance in each of the mechanisms such as the photo-taking lens feeding mechanism and the shutter mechanism. It is usual that errors present in one mechanism are different from those in other mechanisms. In order that the blade opening and closing ring 13 is correctly combined with the photo-taking lens feeding mechanism and the shutter mechanism, having different errors from each other, a final position setting operation of the position switch 25 must be manually adjusted for each camera by trial and error.
The manual operation with adjustment, however, would be a major factor to increase the production cost on the one hand and a cause to impede the automatic assembling of a camera on the other hand.
The technique as disclosed in Japanese Laying-open (Kokai) Patent Application No. 60-235125 can be successfully applied to a pulse-controlled camera of a type in which only the shutter device is controlled and driven by a single step motor. However, this device cannot be applied there as is to a pulse-controlled camera of a type in which the photo-taking lens feeding operation and the shutter blade opening and closing operation are successively carried out by a forward motion and a backward motion of a single basic reciprocating member and the basic reciprocating member is driven by a single step motor, as in the present invention.
The failure of the application of this device here is caused by mechanical errors such as tolerance occurring in the production of mechanical parts and in assembling thereof.
The mechanical errors in machining are inevitably made in production of the moving member as the mechanical part, the sensor means for detecting a displacement amount and a stop position of the mechanical moving member. Such errors caused could allow appearance of sensor means which cannot detect the reference position of the moving member in a pulse width of the drive pulses.
If the sensor means, having such detection precision, is used to detect the reference position of the moving member as in the present invention, the moving member would fail to be correctly set at the reference position thereof in the technique as disclosed in Japanese Laying-open (Kokai) Patent Application No. 60-235125.
If the sensor means, having such detection precision, is used together with the technique as disclosed in Japanese Laying-open (Kokai) Patent Application No. 60-235125 arranging to secure the detection of the reference position of the moving member in any circumstance, the reference position of the moving member must be formed in width of at least one pulse or more. Such an arrangement, however, can permit detection about whether the moving member is located in the proximity of the reference position, but cannot permit detection about whether the moving member is correctly located at the reference position.
It should be understood that it is difficult to apply the technique as disclosed in Japanese Laying-open (Kokai) Patent Application No. 60-235125 having such an antinomic problem as described to the pulse-controlled camera as in the present invention, simply as it is.
A simple increase in pulse rate of motor control may not be sufficient in precision to increase the operation speed of the photo-taking sequence to a high speed.
For example, in a camera conducting the exposure control using shutter blades also serving as a stop, has a stop aperture formed by forcedly stopping the opening operation of the shutter blades in the middle thereof, so that the setting precision of timing to stop the opening operation of the shutter blades and the dispersion of mechanical operation delay are directly related to the precision in forming the aperture.
In this case, as the opening speed of the shutter blades becomes slower, the setting precision of the stop timing increases and the dispersion of the mechanical operation delay becomes smaller. Thus, the low opening speed of the shutter blades would be advantageous in view of the precision.
Accordingly, the shortening of the operation time must be considered taking into account the operation precision of the photo-taking sequence. The technique as disclosed in Japanese Laying-open (Kokai) Patent Application No. 62-257136 as described above lacks such consideration, and, therefore, the technique cannot be applied to the pulse-controlled camera as in the present invention, as it is.
If a camera is operated at a high precision, another problem would occur in relation with the production cost.
Since the mechanical means to conduct the lens feeding operation and the opening and closing operation of the stop and shutter blades are made by combining mechanical members, it is usual that production errors and assembling errors are made in machining and assembling of the mechanical members.
If the operation precision of camera is maintained at a high precision by suppressing errors in production as much as possible by increasing the machining precision of the mechanical members and the assembling precision thereof, the production cost would be extremely increased. Therefore, a novel method is desired to appear to enable the high precision of camera while preventing the increase in production cost.